Parameters of carbon labelling using ionized gases

We have recently described a rapid non-synthetic method for producing¹⁴C-and¹¹C-labelled biomolecules. The apparatus consists of a high vacuum system in which small amounts of¹⁴CO gas are ionized by electron impact. The resulting ionized, excited and dissociated species drift toward a thin layer of organic molecules where they interact to produce¹⁴C-labelled compounds. In this paper, details are given on the mechanisms of interaction of the electron beam and on the parameters influencing the labelling yields. Using cholesterol as a model compound labelling yields were measured while the electron energy, thickness of the organic film, gas pressure and time of exposure were varied over a wide range. The results suggest that¹⁴C⁺ and/or¹⁴CO⁺ are the principal species involved in the labelling reactions. Supported by the Medical Research Council of Canada Grant MA-6137.     

Catalysis of thermal exchange reactions between carboxyl groups and14CO2

The rate of thermal exchange reactions between carboxyl groups and¹⁴CO₂ increases in the presence of catalytic amounts of alkali malonates. This catalytic effect can be utilized for preparative purposes also in the synthesis of¹¹C-labelled aliphatic carboxylic acids from¹¹CO₂.     

Characteristics of a simultaneous sampling system for the speciation of atmospheric T and 14C, and its application to surface and soil air

A simultaneous sampling system for the speciation of atmospheric T and ¹⁴C has been developed. Firstly tritiated moisture together with all water vapor in air is adsorbed on Drierite after coagulation using an electric cooler. Then ¹⁴CO₂ plus stable CO₂ in the dried air is adsorbed on molecular sieve 4A. Elemental tritium gas (HT) plus hydrogen gas (H₂) in the atmosphere along with H₂ gas generated from electrolysis of groundwater which does not contain any T, are oxidized on Pd catalyst to water and adsorbed on molecular sieve 3A. Tritiated methane (CH₃T) and ¹⁴CH₄ plus stable methane in the atmosphere are oxidized on Pt catalyst to water and CO₂ under 400 °C. Then, Drierite and molecular sieve 4A adsorb the oxidized T (HTO) and C-14 (¹⁴CO₂), respectively. Tritium and C-14 in surface and soil air have been measured using this system     

Carbon-14 labelling of biomolecules induced by14CO ionized gas

Ionized¹⁴CO gas provides a rapid method for producing¹⁴C-labelled biomolecules. The apparatus consists of a high vacuum system in which a small amount of¹⁴CO is ionized by electron impact. The resulting species drift towards a target where they interact with the molecule of interest to produce¹⁴C-labelled compounds. Since the reaction time is only 2 minutes, the method is particularly promising for producing tracer biomolecules with short-lived¹¹C at high specific activities. We have studied the applicability of the method to various classes of compounds of biological importance, including sterids, alkaloids, prostaglandins, nucleosides, amino acids and proteins. All compounds treated gave rise to¹⁴C addition and degradation products. Furthermore, for some compounds, chromatographic analysis in multiple systems followed by derivatization and crystallization to constant specific activity, indicated that carbon exchange may occur to produce the labelled, but otherwise unaltered substrate in yields of the order of 10–100 mCi/mol. More conclusive proof of radiochemical identity must await production of larger quantities of material and rigorous purification including at least two different chromatographic techniques. Supported by the Medical Research Council of Canada Grant MA-6137, and by the Banting Research Foundation.     

Quartz Rod Coated with Modified Silica Gel as a Source of CO and CO2 for Standard Gaseous Mixtures

Quartz rods coated with a thin layer of chemically modified silica gel have been used for the generation of a two-component gaseous standard mixture containing carbon monoxide and carbon dioxide. A new method based on thermal decomposition of immobilized compounds chemically bonded to the surface of silica gel has been used in the generation process. The oxalic acid moiety bonded to the glycydoxypropylsilylated surface of silica gel underwent decarbonylation and decarboxylation at 300°C, yielding carbon monoxide and carbon dioxide. On-line connection of a thermal desorber with the GC/FID enabled calibration of the detector following the process of methanization of CO and CO₂. The following amounts of CO and CO₂ were generated per unit length of the rod: 15.1 × 10⁻⁸ Mol cm⁻¹ (RSD = 5.71%) for CO and 34.2 × 10⁻⁸ Mol cm⁻¹(RSD = 5.16%) for CO₂.     

Optimization of preconcentration and isolation for the determination of 15 phenols by supercritical-fluid extraction and gas chromatography with metallomesogenic stationary phase

Based on the merits of well-established capillary gas chromatography (GC), metallomesogenic polymer was used as the stationary phase and flame ionization detector (FID) was used as the detector, the analysis of phenolic compounds explored the possibility of application in complex matrices. We proposed the method combined supercritical-fluid extraction (SFE) of phenolic compounds, which had been enriched on the solid supports of XAD-4 resins, and then with their determinations by capillary GC-FID. The SFE parameters suitable for 15 phenols simultaneously adsorbed onto XAD-4 resins in aqueous solution were assessed by a 4⁵ factorial design method. The best results were 5 min static time, 10 min dynamic time, 0.25 ml methanol spiked, 80 °C oven temperature and 410 atm CO₂ pressure. Also, other parametric conditions for specific phenols were revealed and analyzed. In the comparison with Soxhlet extraction with regard to the recoveries and reproducibility, the developed SFE was quite superior and helped to reduce the detection limit of aqueous samples to 10⁻²-fold. Eventually, the polluted soils near a pharmaceutical factory were primarily tested and given the probable distribution.     

Can gas chromatography combustion isotope ratio mass spectrometry be used to quantify organic compound abundance?

Quantifying the concentrations of organics such as phospholipid fatty acids (PLFAs) and n‐alkanes and measuring their corresponding ¹³ C/¹² C isotope ratios often involves two separate analyses; (1) quantification by gas chromatography flame ionisation detection (GC‐FID) or gas chromatography/mass spectrometry (GC/MS), and (2) ¹³ C‐isotope abundance analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC‐C‐IRMS). This requirement for two separate analyses has obvious disadvantages in terms of cost and time. However, there is a history of using the data output of isotope ratio mass spectrometers to quantify various components; including the N and C concentrations of solid materials and CO₂ concentrations in gaseous samples. Here we explore the possibility of quantifying n‐alkanes extracted from sheeps' faeces and fatty acid methyl esters (FAMEs) derivatised from PLFAs extracted from grassland soil, using GC‐C‐IRMS. The results were compared with those from GC‐FID analysis of the same extracts. For GC‐C‐IRMS the combined area of the masses for all the ions (m/z 44, 45 and 46) was collected, referred to as 'area all', while for the GC‐FID analysis the peak area data were collected. Following normalisation to a common value for added internal standards, the GC‐C‐IRMS 'area all' values and the GC‐FID peak area data were directly compared. Strong linear relationships were found for both n‐alkanes and FAMEs. For the n‐alkanes the relationships were 1:1 while, for the FAMEs, GC‐C‐IRMS overestimated the areas relative to the GC‐FID results. However, with suitable reference material 1:1 relationships were established. The output of a GC‐C‐IRMS system can form the basis for the quantification of certain organics including FAMEs and n‐alkanes. Copyright © 2011 John Wiley & Sons, Ltd.     

Negative ion chemical ionization mass spectrometry of some nitroso compounds with CO2 as reagent gas

Summary Mass spectra of seven N-nitrosamines and five alkyl nitrites, the O-nitroso compounds, have been obtained by low pressure negative chemical ionization with CO₂ as reagent gas. Intense anions were observed at m/z M–32 for N-nitrosamines and at m/z M–30 for alkyl nitrites. Addition products were found at m/z M+12 and M+43 for N-nitrosamines and at m/z M+14 for alkyl nitrites. By using isotopically labeled CO₂, it could be shown that the anions at m/z M+12, M+14 and M+43 correspond to [M - H₂NO + CO₂ ^–, [M – NO + CO₂]^–, and [M – H + CO₂]^–, respectively.

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Negativionen-CI-Massenspektrometrie einiger Nitrosoverbindungen mit CO₂ als Reagensgas

Zusammenfassung Die Massenspektren von sieben N-Nitrosaminen und fünf Alkylnitriten (O-Nitrosoverbindungen) wurden durch negative chemische Ionisation bei niederem Druck mit CO₂ als Reagensgas erhalten. Intensive Anionen wurden bei m/z M–32 für N-Nitrosamine und bei m/z M–30 für Alkylnitrite beobachtet. Additionsprodukte fanden sich bei m/z M+12 und M+43 für N-Nitrosamine sowie bei m/z M+14 für Alkylnitrite. Mit Hilfe von Isotopen-markiertem CO₂ konnte gezeigt werden, daß die Anionen bei m/z M+12, M+14 und M+43, [M – H₂NO + CO₂]^–, [M – NO + CO₂]^– bzw. [M – H + CO₂]^– entsprechen.

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A full account of this work including the negative chemical ionization mass spectra obtained with other reagent gases will be submitted to the Journal of Mass Spectrometry.     

基于TiO2的绿色多相催化剂催化CO2与环氧化合物偶联反应

金属离子掺杂纳米TiO2(M-TiO2,M=Zn2+,Cu2+,Co2+,Mn2+,Ni2+)在CO2与环氧化合物的偶联反应中表现出较高的催化活性.反应以四正丁基碘化铵(TBAI)为共催化剂,在无溶剂条件下进行.考察了反应温度、反应时间和CO2压力在Zn-TiO2/TBAI体系中对反应性能的影响.作为无毒的多相催化剂,Zn-TiO2可循环使用5次,其催化活性没有明显降低.     

Sample treatment techniques for the determination of environmental radiocarbon in a nuclear power station area

This report describes the environmental sample treatment techniques for¹⁴C measurement with liquid scintillation counter. The groundwater sample of about 80 liters was collected from well and inorganic carbon was removed by acidification and recirculated gas stripping with the extraction efficiency of more than 98%. The biological samples were freeze-dried and combusted to carbon dioxide in high pressure combustion unit with a combustion efficiency of nearly 99%. The¹⁴CO₂ in the stack effluents was collected by an air bubbler with a collection efficiency of more than 99% for a sampling time of two weeks. Sampling of¹⁴C in reduced form also has been done by passing the gases through a tube furnace with Pt/Al and Pd/Al catalyst. Active and passive sampling methods for atmospheric¹⁴C measurements were compared in detail, and it could be concluded that the uncertainty associated with passive sampling method was quite acceptable for environmental monitoring. The CO₂ trapped in NaOH was precipitated as BaCO₃, and subsequently reconverted to CO₂ for environmental samples and transferred to Carbo-Sorb E^TM for liquid scintillation counting. In case higher precision is the deciding factor, benzene synthesis would be employed with home-made benzene synthesizer.     

An injection method for measuring the carbon isotope content of soil carbon dioxide and soil respiration with a tunable diode laser absorption spectrometer

We present a novel technique in which the carbon isotope ratio (δ¹³C) of soil CO₂ is measured from small gas samples (<5 mL) injected into a stream of CO₂‐free air flowing into a tunable diode laser absorption spectrometer (TDL). This new method extends the dynamic range of the TDL to measure CO₂ mole fractions ranging from ambient to pure CO₂, reduces the volume of sample required to a few mL, and does not require field deployment of the instrument. The measurement precision of samples stored for up to 60 days was 0.23‰. The new TDL method was applied with a simple gas well sampling technique to obtain and measure gas samples from shallow soil depth increments for CO₂ mole fraction and δ¹³C analysis, and subsequent determination of the δ¹³C of soil‐respired CO₂. The method was tested using an artificial soil system containing a controlled CO₂ source and compared with an independent method using the TDL and an open soil chamber. The profile and chamber estimates of δ¹³C of an artificially produced CO₂ flux were consistent and converged to the δ¹³C of the CO₂ source at steady state, indicating the accuracy of both methods under controlled conditions. The new TDL method, in which a small pulse of sample is measured on a carrier gas stream, is analogous for the TDL technique to the development of continuous‐flow configurations for isotope ratio mass spectrometry. While the applications presented here are focused on soil CO₂, this new TDL method could be applied in a number of situations requiring measurement of δ¹³C of CO₂ in small gas samples with ambient to high CO₂ mole fractions. Copyright © 2010 John Wiley & Sons, Ltd.     

Rapid monitoring of intermediate states and mass balance of nitrogen during denitrification by means of cavity enhanced Raman multi-gas sensing

The comprehensive investigation of changes in N cycling has been challenging so far due to difficulties with measuring gases such as N₂ and N₂O simultaneously. In this study we introduce cavity enhanced Raman gas spectroscopy as a new analytical methodology for tracing the stepwise reduction of ¹⁵N-labelled nitrate by the denitrifying bacteria Pseudomonas stutzeri. The unique capabilities of Raman multi-gas analysis enabled real-time, continuous, and non-consumptive quantification of the relevant gases (¹⁴N₂, ¹⁴N₂O, O₂, and CO₂) and to trace the fate of ¹⁵N-labeled nitrate substrate (¹⁵N₂, ¹⁵N₂O) added to a P. stutzeri culture with one single measurement. Using this new methodology, we could quantify the kinetics of the formation and degradation for all gaseous compounds (educts and products) and thus study the reaction orders. The gas quantification was complemented with the analysis of nitrate and nitrite concentrations for the online monitoring of the total nitrogen element budget. The simultaneous quantification of all gases also enabled the contactless and sterile online acquisition of the pH changes in the P. stutzeri culture by the stoichiometry of the redox reactions during denitrification and the CO₂-bicarbonate equilibrium. Continuous pH monitoring – without the need to insert an electrode into solution – elucidated e.g. an increase in the slope of the pH value coinciding with an accumulation of nitrite, which in turn led to a temporary accumulation of N₂O, due to an inhibition of nitrous oxide reductase. Cavity enhanced Raman gas spectroscopy has a high potential for the assessment of denitrification processes and can contribute substantially to our understanding of nitrogen cycling in both natural and agricultural systems.     

Tritium assay of labelled organic compounds by the flow monitoring counter

Summary A sensitive, simple and cheap counting system for the radioactivity assay of tritiated organic compounds is described. The organic labelled material was converted into carbon dioxide and tritiated hydrogen in an ignition-reduction quartz tube filled with copper oxide and iron fillings. Tritiated hydrogen was then assayed while passing through a flow monitoring counter described earlier [1]. Application of the described counting system greatly decreased the analysis time as compared with other techniques in which internal filling gas counters were used. Results showed that the counting system could readily measure activities as low as fractions of a nCi per mg of tritiated organic compound. The counting system could be used for the assay of organic compounds doubly labelled with tritium and carbon-14.

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Zusammenfassung Eine empfindliche, einfache und nicht kostspielige ZÄhlvorrichtung zur AktivitÄtsbestimmung tritierter organischer Verbindungen wird beschrieben. Die markierte organische Substanz wird durch Erhitzen in einem mit Kupferoxid und EisenspÄnen gefüllten Quarzrohr zu CO₂ und tritiertem Wasserstoff umgesetzt, der durch einen bereits früher [1] beschriebenen Durchflu\zÄhler geleitet wird. Im Vergleich zu anderen Methoden kann mit der empfohlenen Vorrichtung die Analysenzeit betrÄchtlich herabgesetzt werden. Bruchteile von 1 nCi/mg können noch gemessen werden. Das Verfahren ist auch für doppelt markierte (³H,¹⁴C) organische Verbindungen brauchbar.

     

GC Methods for the Determination of Methanol and Ethanol in Insulating Mineral Oils as Markers of Cellulose Degradation in Power Transformers

Methanol and ethanol in transformer oils have been recently proposed as new markers of thermal and mechanical degradation of cellulose (the solid insulation in power transformers). In this work, we optimized and compared the performance of two headspace gas chromatographic methods based on flame ionization (HS–GC–FID) and mass spectrometry detection (HS–GC–MS) to determine methanol and ethanol in insulating mineral oil. For methanol and ethanol, the detection limits were 12 and 27 μg kg^?1 (HS–GC–FID) and 1.3 and 3.1 μg kg^?1 (HS–GC–MS). Repeatability was evaluated in transformer oils for both the methods at different concentration levels of analytes and RSD values were found to lie between 1.8 and 16 %. The accuracy of the methods was assessed under a proficiency test (Cigré JWG A2/D1.46). The methods were compared by a F-test and a one-sided paired t test performed on 21 transformer oils in service. Correlations of methanol and ethanol content in sampled oils against their actual time of service are provided. For each sample, the content of traditional markers (furan-2-carbaldehyde and CO₂) was also measured, finding a correlation between light alcohols and CO₂ content. This indicates that methanol and ethanol determination may be helpful in providing further information on the thermal degradation conditions of transformers’ solid insulation. The method developed is currently routinely applied by the laboratories of Sea Marconi Technologies for the assessment of transformers’ conditions.     

STUDIES OF MECHANISM OF 2-METHYLTHIOPHENE AND THIOPHENE FORMATION FROM N-PENTANE AND HYDROGEN SULPHIDE USING 14C

Abstract

The mechanism of 2-methylthiophene formation from n-pentane and hydrogen sulphide over Cr-containing oxide catalyst is studied by using the Kinetic-Isotope method. The experiments were carried out in pulse system in He as a carrier gas (535° and 3 atm.) using ¹⁴C-labelled pentene and n-pentane. The reaction products were analyzed by radiochromatography. It is shown the 2-methylthiophene formation from n-pentane and hydrogen sulphide proceeds largely via consecutive dehydrogenation of n-pentane to pentenes, pentadiene followed by interaction with hydrogen sulphide. Thiophene is largely as a result of C₄-hydrocarbon interaction with hydrogen sulphide. A general scheme of the mechanism of 2-methylthiophene and thiophene formation is suggested.     

Directing the Structural Features of N2‐Phobic Nanoporous Covalent Organic Polymers for CO2 Capture and Separation

A family of azo‐bridged covalent organic polymers (azo‐COPs) was synthesized through a catalyst‐free direct coupling of aromatic nitro and amine compounds under basic conditions. The azo‐COPs formed 3D nanoporous networks and exhibited surface areas up to 729.6 m² g^?1, with a CO₂‐uptake capacity as high as 2.55 mmol g^?1 at 273 K and 1 bar. Azo‐COPs showed remarkable CO₂/N₂ selectivities (95.6–165.2) at 298 K and 1 bar. Unlike any other porous material, CO₂/N₂ selectivities of azo‐COPs increase with rising temperature. It was found that azo‐COPs show less than expected affinity towards N₂ gas, thus making the framework “N₂‐phobic”, in relative terms. Our theoretical simulations indicate that the origin of this unusual behavior is associated with the larger entropic loss of N₂ gas molecules upon their interaction with azo‐groups. The effect of fused aromatic rings on the CO₂/N₂ selectivity in azo‐COPs is also demonstrated. Increasing the π‐surface area resulted in an increase in the CO₂‐philic nature of the framework, thus allowing us to reach a CO₂/N₂ selectivity value of 307.7 at 323 K and 1 bar, which is the highest value reported to date. Hence, it is possible to combine the concepts of “CO₂‐philicity” and “N₂‐phobicity” for efficient CO₂ capture and separation. Isosteric heats of CO₂ adsorption for azo‐COPs range from 24.8–32.1 kJ mol^?1 at ambient pressure. Azo‐COPs are stable up to 350 °C in air and boiling water for a week. A promising cis/trans isomerization of azo‐COPs for switchable porosity is also demonstrated, making way for a gated CO₂ uptake.     

14CO2 and CO2 Transport in polycarbonate: Measurement of the time lag and permeability

Transport of CO₂ across polycarbonate films has been studied using a diffusion cell technique employing a radioactively labelled tracer (¹⁴CO₂). Because the ¹⁴CO₂ driving force could be established independently of the unlabelled CO₂ driving force, several classes of experiments not possible with conventional techniques were performed. These different classes of experiments showed measurably different time lags. Formally, these experiments all are limiting cases of the more general mixed-gas permeation problem; however, simplifying assumptions in the dual sorption theory are possible because the tracer concentration approaches zero and because the two species in this special mixed-gas problem exhibit the same dual sorption parameters. These simplifications allow derivation of analytical expressions for the time lag for both the unlabelled and labelled gas species. The experimental measurements are in good agreement with the dual sorption model formulated for the mixed-gas tracer diffusion problem.     

Heterogeneous recombination of O + CO on solid CO2 at 77 K

Heterogeneous recombination of O + CO → CO₂ over a solid CO₂ surface at 77 K was investigated. A modified discharge flow setup was used to generate low O atom concentrations by the reaction N + NO → N₂ + O(³P). The O atom concentrations were measured upstream and downstream of the solid CO₂ substrate using resonance fluorescence by monitoring the unresolved 130.3 nm triplet transition ³S₁ ? ³P_2,1,0 at the two fixed points. CO₂ formed was determined by measuring the β activity from C¹⁴O₂ produced from CO containing C¹⁴O as a reactant gas. The CO₂ formation was found to be first order in CO and independent of O atom concentration over the entire range of 4.3 × 10¹² to 1.9 × 10¹⁴ cm^?3 and 1.2 × 10¹¹ to 5.6 × 10¹² cm^?3 for CO and O respectively. The first order recombination coefficient, λ_CO was found to be 1.4 (±.38) × 10^?5.     

Nuclear spin relaxation dynamics of 13CO2 sorbed in polyisobutene rubber

Recently we presented the dynamics of ¹³CO₂ molecules sorbed in silicone rubber (PDMS) ascertained from spin relaxation experiments. Results of a similar investigation for ¹³CO₂ sorbed in polyisobutene (PIB) are presented in this report. The spin-lattice and spin-spin relaxation times as well as nuclear Overhauser enhancements (NOE) were determined as a function of temperature and Larmor frequency. The relaxation mechanisms found to be important for ¹³CO₂/PIB system are intermolecular dipole-dipole relaxation and chemical shift anisotropy with a minor contribution from spin rotation relaxation. We have determined the parameters which characterize correlation times for ¹³CO₂ collisional motion, rotational motion, and translational motions in the PIB. The self-diffusion coefficient of 5.15 × 10^?8 cm²/s obtained from the nuclear magnetic resonance (NMR) data is close to the literature value of the mutual diffusion coefficient of CO₂ in PIB at 300 K obtained from permeability measurements. In contrast to the case of CO₂/PDMS in which a broad distribution (characterized by a fractional exponential correlation function of the Williams-Watts type with α = 0.58) is observed, a sharp distribution with a fractional exponent, α, of 0.99 is found for the CO₂/PIB system. Instead of assuming an Arrhenius type temperature dependence, we used a Williams-Landel-Ferry type temperature dependence and found it to be better suited to describe the behavior of this system. PIB is a densely packed “strong” chain polymer which responds gradually to the temperature variation and gas sorption. In contrast PDMS is a relatively loosely packed “fragile” polymer with a propensity to exhibit rapid dynamic responses to the temperature change and gas sorption. © 1993 John Wiley & Sons, Inc.     

Turning it off! Disfavouring hydrogen evolution to enhance selectivity for CO production during homogeneous CO2 reduction by cobalt–terpyridine complexes

Understanding the activity and selectivity of molecular catalysts for CO₂ reduction to fuels is an important scientific endeavour in addressing the growing global energy demand. Cobalt–terpyridine compounds have been shown to be catalysts for CO₂ reduction to CO while simultaneously producing H₂ from the requisite proton source. To investigate the parameters governing the competition for H⁺ reduction versus CO₂ reduction, the cobalt bisterpyridine class of compounds is first evaluated as H⁺ reduction catalysts. We report that electronic tuning of the ancillary ligand sphere can result in a wide range of second-order rate constants for H⁺ reduction. When this class of compounds is next submitted to CO₂ reduction conditions, a trend is found in which the less active catalysts for H⁺ reduction are the more selective towards CO₂ reduction to CO. This represents the first report of the selectivity of a molecular system for CO₂ reduction being controlled through turning off one of the competing reactions. The activities of the series of catalysts are evaluated through foot-of-the-wave analysis and a catalytic Tafel plot is provided.